This invention relates to a process and apparatus for providing breathing gas for occupants of pressurized cabins in aircraft by the passing of air through adsorbers for increasing the oxygen concentration thereof.
Such a process is shown, for example, in DOS [German Unexamined Laid-Open Application] No. 2,837,281 wherein compressed air is conducted through an adsorber for increasing the oxygen concentration by means of the preferential adsorption of nitrogen on an appropriate adsorbent, and wherein the quantity of the gas flowing through the adsorber, the cycle time, the adsorption pressure, and the ratio of adsorption to desorption pressure are controlled for adjusting the oxygen concentration in a way such that it increases with an increase in flight altitude while simultaneously, the total amount of breathing gas (expressed in Normal liters or Nl) is reduced.
To overcome the difficulties attendant to the prior art breathing gas supply systems such as a cutoff of the air supply, e.g., by inactivation of the air conditioning system or a sudden pressure drop in the cabin due to a leak, an emergency supply of so-called high-altitude breathing oxygen is required in addition to the conventional systems supplied. The emergency supply is provided either by pressurized oxygen bottles or by the gasification of a liquid stock (see in this connection SAFE, 13th Annual Conference 1975, Advanced Aircraft Oxygen Systems, A. J. Aducci). The percentage of oxygen in the emergency supply generally consists of about 99.5% oxygen. However, these containers occupy a relatively large amount of space, especially in the restricted flight cabins normally found in military aircraft. Another problem is that these types of emergency supply systems require separate controls and servicing.